Dissolved oxygen in feed water of a boiler and a steam generator is a factor causing corrosion of a boiler body, a heat exchanger and an economizer arranged upstream of the boiler, and a steam and condensate return line. To inhibit the corrosion, it is necessary to give an oxygen reduction treatment for removing the dissolved oxygen in the water.
As oxygen reduction treatment technique, there are physical treatment technique and chemical treatment technique. Conventionally, the oxygen reduction is carried out by the chemical treatment technique alone or a combined treatment using both the physical treatment technique and the chemical treatment technique simultaneously. As for the physical treatment technique, deaeration treatment by a heat deaerator, a membrane deaerator, or the like has been widely employed. As for the chemical treatment technique, a method of adding an oxygen scavenger, such as hydrazine, sodium sulfite, or saccharide, such as glucose, has been widely employed. Sodium sulfite and saccharide are nonvolatile compounds, and they concentrate as a solid content in the boiler water of a boiler and a steam generator and increase the electrical conductivity greatly. On the other hand, since hydrazine is a volatile compound and does not concentrate in the boiler water, hydrazine has been employed in order to keep the solid content concentration low.
Since a question that hydrazine may be harmful to the human body arose, carbohydrazide (JP 1511025), oxime compounds (JP 1449004), hydroxylamine compounds (JP S58-28349B), heterocyclic compound having N-substituted amino group (JP 3287243), have been proposed as alternative volatile oxygen scavengers to hydrazine in recent years.
Among the conventional alternative volatile oxygen scavengers to hydrazine as mentioned above, since carbohydrazide forms hydrazine at high temperature, it was not a fundamental solution of alternative to hydrazine.
The other alternative volatile oxygen scavengers to hydrazine have the following problems.
Though a typical example of oxime compounds is methyl ethyl ketoxime, this compound has a slow oxygen reduction rate and can absorb few amount of oxygen per unit weight so that this compound is required to be added in a large amount.
Though a typical example of hydroxylamine compounds is diethylhydroxylamine, this compound has a slow oxygen reduction rate and can absorb few amount of oxygen per unit weight so that this compound is required to be added in a large amount.
Though typical examples of heterocyclic compound having N-substituted amino group include 1-aminopyrrolidine and 1-amino-4-methylpiperazine, 1-aminopyrrolidine exhibits rather poor oxygen reduction effect under high pressure condition compared to that under low pressure condition, and 1-amino-4-methylpiperazine exhibit rather slow oxygen reduction rate under low temperature condition.